"He wanted to go back (home) and think it over," Rams general manager Billy Devaney told the newspaper Monday. "We're just taking it one step at a time right now."
Westbrook, 30, suffered two concussions last season with the Philadelphia Eagles, who released him this offseason despite his standing as the franchise's career leader in yards from scrimmage (9,785). He also ranks second in rushing yards (5,995) and third in receptions (426).
After suffering his first concussion Oct. 26 against the Washington Redskins, Westbrook missed two games, then returned for a Nov. 16 contest in San Diego. However, Westbrook suffered another concussion against the Chargers and didn't return until Week 16.
Westbrook, who also has dealt with knee, rib, ankle and foot injuries over the years, said he returned too soon from his first concussion.
The Associated Press contributed to this report.